Wireless local area network (LAN) equipment operating in a 5 GHz band may have dynamic frequency selection (DFS) capability based on European Radio Communications Committee decision. Wireless LAN (WLAN) and radar equipment operating at the 5 GHz band may interfere with each other when operating at the same frequencies and within the operating range. In order to protect radar operation, the WLAN system or device should detect radar signals first to avoid collision with radar channel during an initiate phase. In addition, the WLAN should periodically re-check the operating channel frequency since the radar source may be moving such as airborne radar.
Implementation of dynamic frequency selection specifies that radar signals having a level of at least −52 dBm should be detected. Next, a response to a detected radar signal should result in a switch to an available channel. A best or better available channel should be selected with uniform spreading over the operating band.
Detecting a radar signal is an issue in implementing dynamic frequency selection since the radar signal characteristics may be different from wireless LAN signal characteristics. Typical radar signal ranges may be:
Signal Bandwidth:0.7 MHz to 150 MHzPulse repetition rate:20–100,000 pulses per secondPulse duration:0.05–100 us
Differences between a communication receiver and a radar receiver include bandwidth and time response. Typical 5 GHz wireless LAN systems such as 802.11a and HiperLAN-II may be designed for a 17 MHz signal bandwidth, and may exhibit severe distortion from interference by a narrow radar pulse. As a result, it is difficult to use the LAN receiver or system to correctly estimate radar signal power for radar signals that may have differing pulse signal durations.